Comparison of the Value and Translucency of Composite Resins

Objectives: To examine and compare the translucency of composite resins with different value in an identical hue and translucency shade category.
Methods: Specimen Preparation: Four shades (A1, A2, A3, A3.5) of nine composite resin materials (Beautifil II [BF], Ceram X One [CX], Estelite Sigma Quick [ES], Esthet X HD [EX], Filtek Z250 [F2], Filtek Z350 XT [F3], Gradia Direct [GD], Herculite [HC], and Tetric N-Ceram [TC]) were selected. Six disk-shaped specimens (1mm-thickness and 6mm-diameter) were prepared for each shade of 9 composite materials using a stainless steel mould.
Measurement of Blue Light Irradiance: Before the light curing was started, the mould was placed at the entry of an integrating sphere (UMBB-150; Gigahertz-Optik, Turkenfeld, Germany). During the curing time, a digital optometer (P-9710; Gigahertz-Optik, Turkenfeld, Germany) measured the transmitted irradiance in real time. The maximum irradiance (I_max, mW/cm²) was recorded.
Measurement of Color and Translucency: Color measurements were made using a colorimeter (CR-321; Minolta Co Ltd, Osaka, Japan). The L*, a*, and b* value of each specimen was recorded against black and white backgrounds, respectively. Translucency parameter (TP) was calculated according to the following formula: TP = [(L*_B - L*_W)² + (a*_B - a*_W)² + (b*_B - b*_W)²]^1/2.
Statistical Analysis: The I_max, TP, L*, a*, and b* values were compared among the different shades within each material, using one-way analysis of variance (ANOVA) followed by Tukey’s post-hoc test. All statistical analyses were performed under 95% confidence level.
Results: All variables (I_max, TP, and L*, a*, and b*) showed significant differences among the shades within each material (P<0.001). When the specimen became darker, The I_max decreased significantly in all of 9 composite materials. However, the aspects of translucency were varied. The TP of BF and HC slightly decreased with the darker shades. ES showed no significant differences of TP among the shades. CX, EX, F2, F3, GD, and TC showed significantly higher TP with the low-value shades.
Conclusions: The translucency of composite resins were differed depending on the shades even if they were in the same hue and translucency category, and it was not correlated with the value; the majority of the composite resins showed higher translucency with the darker shades.